A method to deal with concave arc surface in stamping process

(1) In ordinary stamping, when the blank is initially pressed by the punch, it will produce elastic warpage and concave arc surface under the punch. If the gap is moderate and the shearing is carried out in time, the elastic warpage will be basically eliminated. When the gap is too large, the blank is severely bent and stretched at the edge, the shear crack is delayed, and the warpage is not eliminated, leaving it on the stamping part as a concave arc surface. When the interlayer film is too small, because the size of the stamping part falling into the hole of the female die is slightly larger than the hole size, the workpiece will be squeezed and warped to form a concave arc surface. The elimination method is to set blank holder device (such as elastic unloading plate) and elastic ejecting device on the stamping die to suppress elastic warpage. When the gap is small, trimming the stamping gap can eliminate the concave arc surface of the workpiece.

(2) The concave arc surface of the workpiece is caused by the reverse taper of the straight wall section of the concave die opening or the small contact area between the ejector plate and the workpiece. The elimination method is to repair the reverse taper of the cavity wall of the female die and replace the ejector plate.

(3) When the shape of the stamping part is complex, the workpiece warps unevenly due to the uneven pressing force around the workpiece. The elimination method is to increase the blank holder force.

(4) When there is oil, air or sundries between the die and the stamping part, the stamping part will also be flexed, especially for thin and soft materials. The elimination method is to pay attention to strengthening the cleaning work. When there is air, an exhaust hole can be designed on the die.